Mexican police have found dangerous radioactive medical material that was unwittingly taken by thieves when they stole a truck.

The International Atomic Energy Agency issued a rare public alert for the stolen truck which was carrying Cobalt-60, a dangerous category one radiation source, which can be used to make a "dirty bomb".

The substance was being transported from a hospital in Tijuana to a waste facility near the Mexican capital.

The truck was found close to where it was stolen outside Mexico City.

The thieves removed the radioactive material from a protective case, exposing them to dangerous levels of radiation then dumped it less than a mile away.

"Both the container and the radioactive source have been located," said Mardonio Jimenez Rojas, an official at Mexico's national nuclear safety commission (CNSNS).

"The radioactive source was removed from its container and was found a kilometre away."

"The thieves were exposed to radiation," he added, saying those exposed to the material could die.

Experts are working on how to secure the radioactive material in a protective container.

Culprits likely to be common thieves

The truck driver says armed men stole his vehicle in the early hours of the morning when he stopped at a gas station in Temascalapa, 35 kilometres north-east of Mexico City.

"Our suspicion is that they had no idea what they had stolen. This is a area where robberies are common," said Fernando Hidalgo, spokesman for the Hidalgo state prosecutor.

Local authorities issued an alert across eight states following the robbery, appealing to those who stole the truck not to attempt to open the canister containing the material.

Officials say the thieves are likely to be common criminals unaware of the truck's radioactive cargo.

Truck hijacking is common in Mexico and the theft occurred in the State of Mexico, which is not a drug cartel stronghold.

Apart from peaceful medical and industrial applications, experts say cobalt-60 can also be used in a dirty bomb in which conventional explosives disperse radiation from a radioactive source.

The International Atomic Energy Agency, which has stepped up calls on member states to tighten security to prevent nuclear and radioactive materials from falling into the wrong hands, made no mention of any such risk in its statement on Wednesday.

The IAEA also did not give details on how much radioactive material was in the vehicle when it was seized.

"At the time the truck was stolen, the (radioactive) source was properly shielded. However, the source could be extremely dangerous to a person if removed from the shielding, or if it was damaged," the IAEA said in a statement.

Cobalt-60 - the most common radioactive isotope of cobalt, a metal - has many applications in industry and in radiotherapy in hospitals.

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